1. Field of the Invention
The present invention relates to the field of photography and, more particularly, to adapters for operatively coupling cameras to microscopes, telescopes and other optical instruments.
2. Description of the Prior Art
The present invention provides an adapter for operatively coupling a camera having automatic exposure control to an optical instrument such as a microscope, telescope, or other optical apparatus having an eyepiece lens for observing an image therethrough.
In a preferred embodiment, the adapter is particularly well suited for use with a battery powered, automated, single lens reflex camera of the self-developing type such as the SX-70 Land Camera marketed by the Polaroid Corporation, Cambridge, Mass.
To operate such an automated camera, the user observes the scene or image to be photographed through the reflex viewing system and adjusts the objective lens for sharp focus. Upon actuating a camera start button, the camera proceeds through an automatic cycle of operation wherein: (1) a normally open shutter closes and a reflex member pivots from a viewing and focusing position to an exposure position; (2) the shutter reopens to begin the exposure phase, the length of which is determined by a light sensing circuit that includes a camera mounted photocell for receiving light from the scene or image being photographed; (3) the light sensing circuit provides a trigger signal whereupon the shutter is closed to terminate exposure; and (4) the film unit is advanced from the exposure position, through a pair of pressure applying rollers, and then out of the camera through a film exit slot, while at the same time, the reflex member is pivoted back to the viewing position, the shutter is reopened, and the operating cycle is automatically terminated.
Adapters for operatively coupling such a camera to microscopes and other optical instruments are disclosed in the prior art. For example, U.S. Pat. No. 3,798,665 describes an adaptor for mounting the camera on one eyepiece tube of a binocular microscope. The adaptor also includes means for directing scene light transmitted through the other eyepiece to the photocell such that the light sensing circuit may automatically control the exposure interval. U.S. Pat. No. 3,721,170 discloses another type of adapter, for use with a monocular microscope, which includes a beam splitter for diverting a portion of the scene light to the camera mounted photocell.
Other adapters for coupling cameras to optical instruments are disclosed in copending applications Ser. Nos. 420,913 and 420,915 filed on Dec. 3, 1973 (now U.S. Pat. Nos. 3,900,858 and 3,898,678 respectively). These disclosures relate to prismatic elements and/or methods for directing scene light to the photocell without diminishing the intensity of light that is available for exposing the film unit.
The prior art adapters serve two functions. The first is to mount the camera on the optical instrument so that the camera objective lens is in optical alignment with the instrument eyepiece. The second function is to provide a light transmission path to the camera mounted photocell. Control over the exposure of the film unit, however, is governed by the automatic exposure control circuit.
It has been found that while the automated cycle of camera operation is well suited for most general picture taking situations, there are special photographic conditions associated with taking photographs through optical instruments that sometimes exceed the limits for which the camera has been programmed.
As noted earlier, the first step in the automated cycle of operation includes the pivotal movement of the reflex member from the viewing and focusing position to the exposure position which is soon followed by the film exposure phase. The reflex member is a rather large (approximately 3" .times. 3") plate-like member having a substantial mass. The rapid acceleration of this mass towards the exposure position imparts substantial kinetic energy to the reflex member which must be dissipated when the member is abruptly stopped at the exposure position.
A substantial portion of the energy is transferred to the internal framework and body of the camera. When the camera is hand held, this energy is in turn absorbed by the user's body. Likewise, if the camera is mounted on a structure having substantial mass, such as a tripod or heavily constructed optical instrument, the energy is transferred to and absorbed by the structure.
However, there are a number of optical instruments that have eyepiece tubes of rather light construction. When the relatively heavy camera is mounted on the end of the tube, and the reflex member pivots to the exposure position, vibrations are induced in the camera/instrument system because the tube lacks sufficient rigidity and mass to either absorb or transfer energy in an efficient manner.
Generally, these vibrations take from 1 to 3 seconds to damp out and may persist into the beginning of the exposure phase thereby causing a blurring of the image formed at the exposure plane. The vibration effect is particularly serious when working at high magnifications. Small movements of the object being observed are magnified proportionately and are displayed as large movements at the camera exposure plane. The blurring effect is also observed at lower magnifications when the object under observation is well illuminated thereby requiring a relatively short exposure interval. Under these conditions, the camera/instrument system may be vibrating for a significant portion of the total exposure interval causing a blurring of the recorded latent image.
Another limitation of the preprogrammed automatic cycle of camera operation comes to light when taking photographs at very low ambient light levels, such as through a telescope or attempting to photograph an object or sample having very low reflectivity or light transmission properties. Under these conditions, relatively long (approximately 1 to 3 minute) exposures are required. Because the above-described camera is intended for general purpose use, it has a maximum exposure interval of approximately 20 seconds. That is, when there is insufficient light for the photocell circuit to produce the exposure terminating trigger signal within the 20-second limit, the exposure phase is automatically terminated at the end of 20 seconds by a preprogrammed timing circuit.
Also, there are certain photographic situations when the photocell will provide erroneous readings because of special properties of the object being observed and/or the unusual nature of the light reflected therefrom or transmitted therethrough. The photocell circuit is programmed to read the average light intensity emanating from the scene or object. When there is, for example, a wide range of contrast, the average reading may not result in an exposure that will capture the details of object that one wishes to observe.